A light-responsive material contains a dye for various purposes. One of these purposes is spectral sensitization.
In the field of silver salts photography, such a spectral sensitizing technique using a dye has been widely developed since it was discovered by H.W. Vogel in 1873. In the filed of photo voltaic effect, the application of such a technique has been studied since Sheppard and others announced their studies on a silver-silver bromide electrode in 1940. The spectral sensitization of a light-responsive material enables the extension of the wave range of light which is responsive to the light-responsive material or a restriction of the wave range to a desired range and therefore is an extremely important technique in the field of light-responsive materials. Thus, the study is spectral sensitization has been widely carried out. The study of the improvement in the spectral sensitizing effect has been of particularly great interest.
One of the methods for improving the spectral sensitizing effect is to increase the amount of the dye used and hence the light absorption so that the available amount of light can be increased. In this case, it goes without saying that an increase in the amount of the dye to be used in the spectral sensitization raises the light absorption. Unfortunately, the spectral sensitizing effect does not always increase proportionally with the amount of the dye used. The spectral sensitizing effect rather begins to drop at a certain point. This fact has been well known since Leermakers and others reported such in 1937. In order to eliminate such a disadvantage, it has been proposed to use spectral sensitizing dyes which are previously arranged in such an order that the farther they are located from the substrate the shorter is the wavelength of light absorbed by them so that the amount of light available for spectral sensitization can be increased (U.S. Pat. Nos. 3,662,317, 3,976,493, and 3,976,640).
However, the above-mentioned method is merely results in improvement in the arrangement of the dyes and thus is not necessarily satisfactory with respect to the spectral sensitization of certain wave ranged. It has therefore been desired to develop a light-responsive material having a spectral sensitivity improved by the use of a novel spectral sensitizer.